Beer fridge...Air line cooler/Plasma.

[TimGa]

Does/will a plasma work more effective on cooler compressed air?

If so, here's my idea.

I have a small beer fridge for my garage. I want to coil some copper tubing, place inside the fridge with lines coming in and going out. I imagine I could get about 20 ft of line in the top part of the fridge...leaving room for some beer. Why do this? I want to cool off the air heading to my plasma...will this benefit me?
Here's a simple breakdown of my layout:

Compressor/40ft copper tubing/Triple air filter/Fridge idea/20ft copper tubing/Couplers(end). Somewhere in there I will also have a ball valve to release collected water. I would have another filter on the back of the plasma.

Somewhere back I seen a picture of a coiled tubing in a tub of water...that's where I got this idea.


Thanx

[Pumpkinhead]

Nope, waste of time for two reasons.
a) All that excessive Cu tube is gonna cut into your air flow, plaz's love lots of air.
2) The only cool air the plaz will see is that first blast of air between pilot arc and plasma, after that the temperature will be the same going in the fridge as out, due to the high volume being used.

[Roger]

Good idea cooling compressed air condenses water that can be filtered out. Your little bear frig doesn't have enough cooling capacity to make it work.

[jimcolt]

Actually this has been done, and it works quite well. Put your coil of 3/8" ID copper in the largest plastic tank of water...inside the fridge. The water kind of stores energy....and helps transfer the cold to the air. Cold air will condense water quite easily. Where the hose runs out of the fridge affix a verticle drop pipe that goes straight down to the floor, and attach a float operated water drain. Tap your air off the highest (near the ceiling) part of that vertical pipe. Most Plasma systems use les than 6 scfm of air......smaller the nozzle, less flow. Leave plenty of room for beer. Maybe you should get a bigger fridge?

Jim Colt

[Pumpkinhead]

And you claim to work for Hypertherm, Eh?

20 feet of 3/8" Cu tube has a volume of 0.015277 ft³ at 6CFM, that's ~400 volume changes per minute, I don't think your gonna get much cooling at that rate.

[Hotfoot]

Tim, I just noticed you were in Saskatchewan...how about a single 1/2" iron water pipe around the outside of your shop (up at gutter level)...wouldn't that be "free cooling" most months of the year? My iron pipe runs 25' up/down a wall and along the ceiling inside my South Texas shop, and I get zero water. I do have two water traps, but they are always dry. I do burp the water out of my tank periodically:)

[jimcolt]

I have been with Hypertherm for over 31 years......why do you ask?

Jim

[enlpck]

Lets do some math:

Specific heat of moist air (uncompressed, but it is close enough at 100PSI) in terms of FREE VOLUME: 0.019BTU/(ft^3*degF), which translates to about 7BTU/(hr degF) at 6CFM. This means, you need 7BTU/hr of cooling to drop 6CFM by one degree.

A small (6Cu ft is the one I am looking at) 'fridge might be capable of 150BTU/hr, s t would be able to drop the air temp by about 21 degF if there is good thermal transfer. A larger fridge (like the one in my kitchen) has in the ballpark of 500BTU/hr capacity, and could drop the same flow rate by about 70 degF.

This is pretty reasonable. Dropping 20deg is enough to condense a lot of water if the starting temp is about 80F. In practice, you might be able to get a 40deg drop if a water bath is used as a reservoir, due to the intermittent airflow of a plasma cutter (even a CNC unit might burn at 50 to 60% duty cycle), and a 40deg drop from 80F is about as far as you would want to go, since you need some temperature differential to get the heat out of the air, and the cooler would not want to be below freezing (32F) to avoid icing in the air line.

Sounds like a small to midsize fridge would be fine for a homebrew cooler.

I might go with several parallel lengths of smaller tubing to increase the heat transfer surface, or a longer length of the 3/8, or even 1/2"

[TimGa]

Good points.

Hotfoot, can't use iron outside here...wouldn't last, it would rust within 6 seasons...but you gave me another idea.
How about if I ran the copper tubing inside the walls of my garage? My garage, 24x24, is not finished. So I could run 3-4 straight runs of 22ft each, 1/2" pipe, back and forth. Add my filters and dump outs, insulate and sheet the inside. Doing this would allow the air in the lines to cool but not freeze. By having roughly 100ft of cool air.................wait a minute, that won't work either...what do I do in the summer? Sometime it get's up to 40 Degrees Celius...that means the walls would be hotter.

I think I'm thinking about this too much...going for a beer.

Thanx for your ideas.

[Roger]

When I lived in NW Washington State city or well water was always cold. Run one copper tube inside another tube or pipe like a beer wort cooler. Make outer tube water inner tube air with counter flow. Discharge water then goes to hose bib watering garden or lawn. This should work year round and be almost free. Dad cooled a house in summer with city water flowing through water/air heat exchanger in furnace air ducting.

[Pumpkinhead]

A small (6Cu ft is the one I am looking at) 'fridge might be capable of 150BTU/hr, s t would be able to drop the air temp by about 21 degF if there is good thermal transfer. A larger fridge (like the one in my kitchen) has in the ballpark of 500BTU/hr capacity, and could drop the same flow rate by about 70 degF.


Lemme get this straight, this 'fridge in your kitchen has the wondrous ability to lower the temperature of 6 cu. ft. of air by 70°F in one minute?

So, you're saying if this magical appliance had an internal volume of 6 ft³ and you sealed it, drew a vacuum in it, on a hot summer day (ambient 100°F), then allowed it to fill with air (again, ambient 100°F), waited a minute, the internal air temperature will be 30°F?

BILGEWATER!!!

And I am being quite generous when I say that, 'cause I could ask if you are purporting that this wondrous appliance could do that every 60 seconds. Because it sure sounds that way.

[enlpck]

You are aware that the abbreviation 'hr' stands for hour, arn't you? As in 500BTU/hr? You understand that the heat for a 1deg change for one cubic foot of air is 0.019BTU? Do the arithmetic. This is the rate of cooling required. 6cubic feet of air isn't much air. Change of state is where the large energy change comes in, but the percentage vapor at the operating pressure (about 100PSI) will be low enough to affect the temp change by only a few degrees (not all of it will condense, and it is a low portion to begin with) as long as the air has already been cooled to ambient.

You might want to adjust the medication, as your attitude seems to be acting up again.



Lemme get this straight, this 'fridge in your kitchen has the wondrous ability to lower the temperature of 6 cu. ft. of air by 70°F in one minute?

So, you're saying if this magical appliance had an internal volume of 6 ft³ and you sealed it, drew a vacuum in it, on a hot summer day (ambient 100°F), then allowed it to fill with air (again, ambient 100°F), waited a minute, the internal air temperature will be 30°F?

BILGEWATER!!!

And I am being quite generous when I say that, 'cause I could ask if you are purporting that this wondrous appliance could do that every 60 seconds. Because it sure sounds that way.

[enlpck]

By the way, pumpkin, allow me to quote you: "BILGEWATER"

This is in response to: "6CFM, that's ~400 volume changes per minute"

You do understand that the 6CFM is 6 STANDARD cubic feet per minute? Uncompressed volume at standard conditions? Compressed to 100PSIG, the volume will be about 0.9CuFt, for about 60 exchanges per minute in the volume given. Still a high rate, but not real bad. A one second timeframe is less than desirable for a large delta-T, but not horrid. I would shoot for about 5 seconds.

[BillyP]

Actually this has been done, and it works quite well. Put your coil of 3/8" ID copper in the largest plastic tank of water...inside the fridge. The water kind of stores energy....and helps transfer the cold to the air. Cold air will condense water quite easily. Where the hose runs out of the fridge affix a verticle drop pipe that goes straight down to the floor, and attach a float operated water drain. Tap your air off the highest (near the ceiling) part of that vertical pipe. Most Plasma systems use les than 6 scfm of air......smaller the nozzle, less flow. Leave plenty of room for beer. Maybe you should get a bigger fridge?

Jim Colt

...would sure make a nice air dryer if nothing else.

[jimcolt]

Contrary to the the disagreement from one poster on this subject....this works very well as an air dryer....for a plasma system that is operating at less than 100% duty cycle.

Jim Colt

[usmcpop]

Some folks use those refrigerators in liquid-cooled computer setups. In one test of commercial cooling fluids, they also tried stale ale, just as a joke. It was the second most effective of the fluids tested. :D

[Sandy]

I have a small beer fridge for my garage. I want to coil some copper tubing, place inside the fridge with lines coming in and going out. I imagine I could get about 20 ft of line in the top part of the fridge...leaving room for some beer. Why do this? I want to cool off the air heading to my plasma...will this benefit me?

I wouldn't do anything that would risk raising the temperature of the beer :eek:.. There's got to be some other way.


Somewhere back I seen a picture of a coiled tubing in a tub of water...that's where I got this idea.

Reminds me of the cooling towers for air conditiong systems in the desert states. Some of the older ones were pretty crude but cheap and effective. I'm sure they have better systems by now but the concept is no doubt the same.

Of course in Canada you wouldn't want anything based on water because of the freezing issues. Nor would you want a seperate system running full time just for occasional plazma use. Turning on a system and waiting for cooling isn't a good option either. Sharing resources with something that's already running could be worthwhile. You'd have to weigh the costs vs effects vs gains.

[Pumpkinhead]

I've previously commented on this material, but it seems to have disappeared.


You are aware that the abbreviation 'hr' stands for hour, arn't you?

Are you aware this punctuation mark (?) means a question has been asked and requires a response?
Because you hadn't answered my two (2) prior queries.




This is in response to: "6CFM, that's ~400 volume changes per minute"

You do understand that the 6CFM is 6 STANDARD cubic feet per minute? Uncompressed volume at standard conditions? Compressed to 100PSIG, the volume will be about 0.9CuFt, for about 60 exchanges per minute in the volume given. Still a high rate, but not real bad. A one second timeframe is less than desirable for a large delta-T, but not horrid. I would shoot for about 5 seconds.

Alright you got me on the compressed gas/changes per minute.

Although I've discussed your FREE VOLUME cooling in my previous post, I'll discuss compressed gas here.
So, in effect, you are saying that if we place a copper sphere (radius 7.2")filled with 100°F air in your 'fridge of the gods' for 1 minute, that when we remove it, the air contained within the sphere will be 30°F?

[Pumpkinhead]

Contrary to the the disagreement from one poster on this subject....this works very well as an air dryer....for a plasma system that is operating at less than 100% duty cycle.

Jim Colt

If this is true (and we know it's not), why isn't it more prevalent?
And why only plasmas? Wouldn't the same bucket o' water work for other dry air users?
Conspiracy pehaps! Big business wanting to sell actual compressed air dryers for hundreds or thousands of dollars, when all it takes is a bucket and some copper tube.

[jimcolt]

Actually you can buy an air dryer from Harbor freight with an included water drain for under $350 (imported of course)....it has a tiny refrigerant system and can handle up to 11 cfm. I know more than a dozen people that use them....and they have had good luck. Or you can buy a Dayton brand unit from Graingers, same flow capacity for about $850...I suspect it may be imported as well.

Or you can make a home built cooler with an old refrigerator....recycling at its best...and produce your own dry air....and for some of us we will keep some beer cold....while others should just stick their heads in the door for a while to chill.

An average home refrigerator has more than adequate cooling capacity for air consumption in a small shop.

Plasma systems will experience better starting, and dramatically longer consumable life with dry air. I'm pretty sure that most pnuematic devices will last longer without moisture in the air as well.

Jim

[TimGa]

If I don't try my idea I won't really know if it works. All parties make good points, thanx for the comments.
Once I complete my garage I'll bring everyone up to date on the data results. Hope to supply pictures as soon as I'm done.

[enlpck]

I've previously commented on this material, but it seems to have disappeared.



Are you aware this punctuation mark (?) means a question has been asked and requires a response?
Because you hadn't answered my two (2) prior queries.




Alright you got me on the compressed gas/changes per minute.

Although I've discussed your FREE VOLUME cooling in my previous post, I'll discuss compressed gas here.
So, in effect, you are saying that if we place a copper sphere (radius 7.2")filled with 100°F air in your 'fridge of the gods' for 1 minute, that when we remove it, the air contained within the sphere will be 30°F?

P-head: Why do you insist on being so obnoxious? Why do you insist on not reading before responding? Do you find education, experience, and knowledge threatening?

Should you read (reading is, after all, fundamental) the previous posts, by Mr. Colt and myself in particular, you will find your questions answered.

But, for the sake of politeness ( http://www.thefreedictionary.com/polite ), I will respond:

Your hypothetical copper sphere is a straw man, presoaked with kerosene, given my statement "if there is good thermal transfer". Such would not occur with the sphere unless there was a transfer medium such as liquid water (not ice, as the thermal conductivity of ice is poor), as well as sufficient temperature differential to effect the heat transfer, due to the small surface area of the sphere relative to the enclosed volume. Your copper sphere will also have significant thermal capacity compared to the air within if made such that it can support itself.

IF, on the other hand, the shell started at a suitable temperature near 30 degrees, and was in the freezer compartment with the compressor running, the freezer compartment being at a temperature sufficiently below 30 degrees so that heat transfer can occur, and the air was instantly exchanged in the sphere for 100 degree air, and sufficient means for air circulation in the sphere, possibly with additional surface to effect heat transfer (refer, again, to my original post), then, at the end of one minute, the conditions would be substantially the same as immediately prior to the exchange of air, with the air being cooled to about 30 degrees, if there was sufficient heat transfer from the outside of the sphere, such as provided by a circulating fan in the freezer or by a water bath with contact to the freezers evaporator. Of course this is with my `fridge of the gods' (GE are the gods? Wow! I never knew. I guess I need to tell the guys at the appliance store that there are people that find deep religious significance in a 22CF side-by-side).

Of course, in an air cooler using small diameter tube (as I said, I would probably go with parallel lengths smaller than 3/8, or use a longer length), if the air flow is constant, a equilibrium will be established (if the inlet temperature is constant). If my `fridge of the gods' was used, then the equilibrium could be established such that, if the inlet air was 100 degrees, the outlet air would be a bit above 30 degrees, being slightly higher due to the heat liberated by the change of state of the moisture as it condenses (see, again, my previous posts).

And by the way, yes, the wondrous unit in my kitchen does have the ability to lower the temperature of 6 cubic feet of air 70 degrees in one minute to a good approximation. Test: the freezer compartment is about 10 cubic feet. It is set at (roughly) 5 degrees. My house is about 7 degrees. Opening the door when it is the usual condition of nearly empty (I don't do a lot of frozen food) and holding it open for about 1/2 minute, the air inside pretty much fully exchanges (cold dense air runs out the bottom, fresh warm air moves in the top. The biggest loss for most homes is opening the door on the unit) The compressor starts. Close the door. The compressor runs for a bit over two minutes, then doesn't run again for nearly and hour. All of the air (70 degree) that entered the unit was cooled to 5 degrees. This is a 65 degree differential per minute for 5 cubic feet. Allowing for other losses (warming of the inside of the door, warming of the lining of the unit, etc, from the target temperature), this is pretty darn close. Definitely in the ballpark. Every time I need to fill that bad boy up, I thank the previous occupant of my home for purchasing the thing right before moving, since my previous 'fridge was about 20 years old and half the size.

Might I suggest a few good books on thermodynamics to you? It is really a wonderful science.

[Pumpkinhead]

P-head: Why do you insist on being so obnoxious? Why do you insist on not reading before responding? Do you find education, experience, and knowledge threatening?

I’m only obnoxious to those who can’t admit they are wrong.
If I responded prior to reading, what would I be responding to?
No, I do not. Yet you find my picking apart your flawed posts threatening, do you think your posts are the be all / end all of knowledge.
Also, I would like to know if your legs get tired from all the back-pedaling you have done?

Your hypothetical copper sphere is a straw man, presoaked with kerosene, given my statement "if there is good thermal transfer…..

IF, on the other hand, the shell started at a suitable temperature near 30 degrees, and was in the freezer compartment with the compressor running, the freezer compartment being at a temperature sufficiently below 30 degrees so that heat transfer can occur, and the air was instantly exchanged in the sphere for 100 degree air, and sufficient means for air circulation in the sphere, possibly with additional surface to effect heat transfer (refer, again, to my original post), then, at the end of one minute, the conditions would be substantially the same as immediately prior to the exchange of air, with the air being cooled to about 30 degrees, if there was sufficient heat transfer from the outside of the sphere, such as provided by a circulating fan in the freezer or by a water bath with contact to the freezers evaporator.

Well, gee!! Why didn’t you say so? That is to say, no shít, Sherlock!! Of course it took you this long
to finally, kind of, sort of, admit your folly. The OP asked if coiling up some Cu tube in his beer fridge would dry his air. I answered that that wouldn’t do it. You and Mr. Colt felt the need to contradict my statement with flawed logic, which, I then called you on. And now you have admitted, that for you prior statements to work, one needs to disassemble his beer cooler ‘fridge and use it’s components to fabricate a proper compressed air dryer.
Well, fück me sideways!!! Why didn’t you just say that in post #8

[Pumpkinhead]

Actually you can buy an air dryer from Harbor freight with an included water drain for under $350 (imported of course)....it has a tiny refrigerant system and can handle up to 11 cfm. I know more than a dozen people that use them....and they have had good luck. Or you can buy a Dayton brand unit from Graingers, same flow capacity for about $850...I suspect it may be imported as well.

...
Jim

HUH????
What on God's green earth does this have to do with my question to you about buckets of water and copper tube?

[jimcolt]

I really see no further need to respond to idiots that insist on making fools of themselves on a public forum, and attempting to hide behind the guise of an orange gourd! I look forward to the original posters progress with his air dryer...made from a refrigerator!

Jim

[Monte55]

Actually he never said he was making an air drier. His question was ...would the plasma cutter work better with cooler air. The answer is NO. Dropping the temp of the air another 40-70 degrees isn't going to make a difference
considering how hot plasma gets.

[jimcolt]

Nick,

I guess you have a point there....although in the original post it was stated that a ball valve would be installed to drain water.....so I likely assumed that he was considering chilling the air as a very effective and common method of separating moisture from that air....and plasma systems will experience longer consumable life, resulting in better cut quality over the life of the consumables.

Jim